MXPA00005201A - Airbag fabric coated with a porosity blocking cross-linked elastomeric resin - Google Patents

Abstract

A coated base fabric for use in an automotive airbag is provided. The coated base fabric includes a substrate of woven nylon or polyester which is overcoated with a porosity blocking layer of a cross-linked elastomeric resin. Such a resin may be, without limitation, selected from the group consisting essentially of polyamide, butyl rubber, EPDM, polyurethane, hydrogenated NBR, acrylic rubbers, and mixtures thereof. The porosity blocking layer of polyamide material is present at a coating weight of between about 0.1 and 0.5 ounces per square yard. Furthermore, the resin may be present as either a latex or in solution with an organic solvent or solvents. A method for producing the coated fabric of the present invention is also provided.

Description

AIR BAG FABRIC COATED WITH A RETICULATED ELASTOMERIC RESIN THAT BLOCKS POROSITY TECHNICAL FIELD This invention relates generally to coated fabrics and more particularly to fabrics for use in automotive restraint cushions having low permeability and yet avoiding the use of heavy coatings such as neoprene, silicone and the like, which have been employed. historically. More specifically, the present invention relates to a coated air bag fabric that includes a very light coating of finely divided stable crosslinked elastomeric resin material dispersed in water. The elastomeric coating is applied across on one or both sides of a nylon or polyester substrate fabric in weights of dry coatings of about 0.6 ounce or less per square yard. All crosslinked elastomeric resins are within the scope of this invention. Polyamides, polyurethanes, and hydrogenated acrylonitrile-butadiene rubbers (hydrogenated NBR), as well as ethylene-propylene-diene comonomer rubber (EPDM), butyl rubber, and acrylic rubber are especially interesting. BACKGROUND OF THE ART Air bags for motor vehicles are known devices and have been used for a substantial period of time. A typical building material for air bags has been a polyester or nylon fabric coated with an elastomer such as neoprene or silicone. The fabric employed in these bags is typically a woven fabric formed of synthetic yarn by weaving practices well known in the art. The coated material has found acceptance since it acts as a barrier impervious to the inflation medium. The inflation medium is generally a nitrogen gas generated from a gas generator or inflation device. Said gas is transported to the cushion at a relatively hot temperature. The coating obstructs the permeation of the fabric by said hot gas, thus allowing the cushion to inflate rapidly without undue decompression during a collision. The airbags can also be formed from uncoated fabrics that have been woven so that a product having low permeability is created or from fabric that has been subjected to a satin treatment to reduce permeability. Fabrics that reduce air permeability by satin or other mechanical treatments after weaving are presented in U.S. Patent No. 4,921,735; U.S. Patent 4,977,016 and U.S. Patent 5,073,418 (all incorporated herein by reference). The coating of a fabric with an elastomer such as, for example, neoprene typically requires the application of the elastomer from a solution in a volatile solvent. This solvent must then be evaporated and the elastomer system must be cured. Weights of dry coatings typical for neoprene are within the range of approximately one ounce per square yard or more. Silicone coatings typically employ either solvent-based reaction systems or complex two-point component application. Dry coating weights for silicone are within the range of approximately 0.7 ounce square or more. As will be noted, a significant addition in weights substantially increases the cost of the base fabric for the airbag and makes it more difficult to sew the fabric eventually into an airbag structure. The use of certain polyurethanes as coatings in accordance with that disclosed in U.S. Patent 5,110,666 to Menzel et al. (which is incorporated herein by reference) allows a low weight addition within a range of 0.1 to 1 ounce per square yard, but the material itself is relatively expensive and is believed to require relatively complex methods of compounding and application due to the nature of the coating materials. Nevertheless, the patent holder employs strictly linear thermoplastic polyurethanes within its coating and allows the presence of 0.5 oz per square yard of said aforementioned coating on the fabric. Such teachings clearly do not anticipate or suggest the required coatings and preferred amounts of said coating in the air bag fabric of the present invention. Taking into account the aforementioned background, it is readily apparent that there is a need for a base fabric for air bag that offers controlled low permeability through the use of a coating that offers an effective barrier to air permeability while avoiding the complexity inherent and the cost of materials used so far. Accordingly, the invention focuses on a coated base fabric for an air bag comprising a polyester or polyamide substrate fabric coated with a porosity blocking layer of a crosslinked elastomeric coating resin. The term "porosity blocking layer" encompasses the amount necessary to obtain a fabric having adequate air permeability characteristics while also offering a coating that passes a separation (or blocking) test on storage. Any stable elastomeric resin within this invention can be employed to the extent that the resin is crosslinked on the surface of the fabric and applied at a coating weight between about 0.1 and 0.5 ounce per square yard of fabric. By stable elastomeric resin, we understand that said resin has a glass transition temperature (Tg) lower than room temperature (i.e., from about 20 to about 25 ° C). Said measurement of glass transition temperature indicates the presence of elastomeric properties for the specific material. It is especially interesting that the cross-linked stable elastomeric resins are polyamides, polyurethanes, hydrogenated NBRs, EPDMs, butyl rubber and acrylic rubbers. When a thin coating of a cross-linked elastomeric resin is added to an air bag fabric, it has been found that said fabric exhibits superior blocking test results as well as necessary and beneficial characteristics of air permeability, especially in comparison with the prior art. . Other objects and advantages of the present invention will be apparent upon reading the following detailed description. The requirement of crosslinking is of extreme importance in this invention since it was discovered that the beneficial properties were obtained only through the use of a crosslinked elastomeric resin. Said crosslinked coating is produced through the addition of a crosslinking agent to the coating formulation or is supplied through the use of a self-crosslinking resin. The self-crosslinking resins provide the necessary mechanical properties (i.e., increased tensile strength) and aging stability for the elastomeric resin coating at the required level of low coating weight. A non-crosslinked resin does not provide such necessary properties. While the invention will be described and presented in relation to certain preferred embodiments and practices, it is not intended in any way to limit the invention to these specific embodiments but is intended to encompass equivalent structures, structural equivalents, and all alternative embodiments and modifications that may be defined by the scope of the appended claims and their equivalents. PRESENTATION OF THE INVENTION As indicated above, in many air bag applications, it is desirable to have a coating to allow rapid and complete inflation of the restriction cushion during a collision. This need for a liner is particularly significant as it relates to bags for lateral impacts and on the driver's side where there is little distance between the occupant and the cushion. Coatings may be particularly important in newly developed curtain type cushion structures where prolonged inflation may be desired (i.e., for several seconds). Such fabrics for air bags must pass certain tests in order to be used within restriction systems. A test of this type is called a blocking test that identifies the force required to separate two parts of a coated fabric between them after a prolonged period of storage in contact with each other (such as in the case of an airbag) . A laboratory analysis for blocking includes pressure of coated sides together of two samples of two inches by two inches of air bag fabric at 5 psi at a temperature of 120 ° C for 7 days. If the force required to separate the two samples after this time is greater than 50 grams per square yard, or if the time required to separate the fabrics using a 50-gram weight suspended from the bottom cloth layer is greater than 10 seconds, the coating does not pass the blocking test. Obviously, the lower the shear force of separation that is required, the more favorable the coating. Another test that the specified coated fabric must pass is the oven aging test. A test of this type also simulates the storage of an air bag fabric over a long period of time when exposed to high temperatures and is actually used to analyze alterations of several different fabric properties after such prolonged storage in a hot oven ventilated (more than 100 ° C) for 2 or more weeks. For the purposes of this invention, the test was basically employed to analyze the air permeability of the coated fabric after storage under a pressure of about 125 Pascais. Air bag fabrics should generally have a level of air permeability of less than about 0.2 cfm to 125 Pa. Again, the lower the air permeability, the better the coating.

Surprisingly, it has been found that a stable cross-linked elastomer resin applied on an air bag fabric surface at a weight between about 0.1 and 0.5 oz per square yard offers a coated fabric that passes both the blocking test and the aging test. in oven with very low air permeability. This unexpectedly beneficial type and amount of coating therefore offers an air bag fabric that is easy to inflate after prolonged storage and will remain inflated for a sufficient period of time to ensure an optimum level of safety within a restricted system. Furthermore, it is evident that the lower the coating composition required, the less expensive the final product becomes. In addition, the lower the coating composition required, the lower the packing volume of the air bag fabric within an air bag device. This benefit therefore improves the packaging of the airbag fabric. The substrate through which the crosslinked elastomeric resin coatings are applied to form the air bag base fabric according to the present invention is preferably a plain woven fabric formed of yarns comprising polyamide or polyester fibers. Said yarn preferably has a linear density of about 210 denier to about 630 denier. Such yarns are preferably formed of multiple filaments where the filaments have equal densities of about 6 denier per filament or less and more preferably about 4 denier per filament or less. Such substrate fabrics are preferably woven using fluid jet weaving machines in accordance with that disclosed in U.S. Patent Nos. 5,503,197 and 5,421,378 to Bower et al. (they are incorporated here by reference). The fabric substrate with the applied coating will be known below as an air bag base fabric. Other possible components present within the crosslinked elastomeric resin coating composition are thickeners, antioxidants, flame retardant agents, coalescing agents, adhesion promoters, and dyes. In accordance with the potentially preferred practices of the present invention, a waterborne microdispersion of finely divided elastomeric resin (such as high crosslinking polyamide resin particles) forms a composite with a thickener and a flame retardant in order to provide a compound mixture having a viscosity of approximately 8000 centipoise or more. The potentially preferred polyamide dispersion is marketed under the trade designation MICROMID® 632 hpl by Union Camp Corporation which is believed to have a place of business in Wayne, New Jersey. Other preferred crosslinked elastomeric resins include polyurethane such as Witcobond® 253 (35% solids), from Witco, and Sancure, from BFGoodrich, Cleveland, Ohio; Hydrogenated NBR, such as Chemisat® LCH-7335X (40% solids), from Goodyear Chemical, Akron, Ohio; EPDM, such as rubber latex EP-603A, from Lord Corporation, Erie, Pennsylvania; butyl rubber, such as, for example, butyl rubber latex BL-100, from Lord Corporation; as well as acrylic rubber (elastomers), such as HyCar®, from BFGoodrich. A potentially preferred thickener is marketed under the trade designation NATROSOL® 250 HHXR by the Aqualon division of Hercules Corporation which is believed to have a place of business in Wilmington, Delaware. The crosslinking agent may be any compound well known in the art, such as melamine formaldehyde, and the like. In order to meet the flame retardant requirements of the Federal Motor Vehicle Safety Standard 302 (Federal Motor Vehicle Safety Standard 302) for the automotive industry, a flame retardant agent is also preferably added to the composite mixture. A potentially preferred flame retardant agent is AMSPERSE F / R51 marketed by Amspec Chemical Corporation, which is believed to have a place of business in Gloucester City New Jersey.

Once the formation of compounds is finished, the formulation is preferably applied by scraping the fabric substrate and drying and cured to form a thin coating. The scraped coating in this sense includes, but is not limited to, blade application, particularly knife application methods on space, floating blade, blade on foam cushion, just to name a few different types of methods. Such scraping coating allows the majority of the coating resin to remain within the interstices of the threads of the airbag fabric. It is within these interstices that air is more likely to leak from an inflated airbag without the presence of coating. In addition, scraping coating allows the application of a very small amount of resin on the raised yarn of the air bag fabric at this low coating weight. As a result, this particular distribution of coating materials on the surface of the air bag fabric allows the crosslinked elastomeric resin coating to seal the fabric while the low weight of the coating also simultaneously limits contact between resin samples placed in portions. different from the surface of the fabric. This feature is very important to ensure that the fabric will pass the required blocking test, described above. The final dry weight of the coating is preferably about 0.4 ounces per square yard or less and more preferably 0.2 to 0.35 ounces per square yard or less. The resulting base fabric is substantially • impermeable to air when measured in accordance with the standards of the DTM7 ASTM "Air Permeability of Textile Fabrics" test. As previously indicated, the substrate fabric is preferably a woven nylon material. In the most preferred embodiment, said substrate web will be formed of nylon 6,6 fibers. It has been found that such polyamide materials exhibit particularly good adhesion and maintenance of hydrolysis resistance when used in combination with the coating according to the present invention.

Preferred mode In order to further describe the present invention, the following non-limiting examples are presented. The polyamide elastomer discussed above and described in greater detail below is the most preferred embodiment of the invention. These examples are provided solely for the purpose of illustrating certain preferred embodiments of the invention and are not to be construed as limiting the scope of the invention in any way. Example 1 A mixture was prepared using the following constituents where all parts are offered by weight. Self-crosslinking polyamide Resin (MICROMID 632 hpl) (35% solids) 100 grams NATROSOL 250 HHXR 2.6 grams Flame retardant (DE-83R, from Great Lakes Chemical Corporation, West Lafayette, IN) 2 grams Water 80 grams The viscosity of the mixture The resultant was approximately 15,000 centipoise in accordance with what was measured in a Brookfield viscometer. This mixture was coated on a 420 denier Nylon 6, 6 air bag fabric substrate using a knife applicator over space and was dried at a temperature of 320 ° F for 3 minutes. The dry coating weight was 0.25 ounces per square yard. The air permeability measured at 125 Pa is 0.0 cfm per square foot of fabric (in accordance with that tested according to ASTM D737 method) and the coating passed the blocking test. Example 2 A mixture was prepared using the following constituents. Witcobond 253 105 grams Crosslinking agent (Aerotex M-3, from Freedom Textile Chemicals Co., Charlotte, North Carolina) 2 grams Flame retardant (DE-83R, from Great Lakes Chemical Corporation, West Lafayette, IN) 2 grams Natrosol 250 2.6 grams Water 80 grams The viscosity of the resulting mixture was approximately 15, 000 centipoise. This mixture was applied to a 420 denier nylon 6,6 air bag fabric substrate using a knife applicator over space and was dried at a temperature of 320 ° F for 3 minutes. The dry coating weight was 0.3 ounce per square yard. The air permeability measured at 125 Pa was 0.0 cfm and this coated fabric passed the blocking test. Example 3 MICROMID 632 hpl (35% solids) 120 parts NATROSOL 250 HHXR 2.5 parts AMSPERSE F / R 51 (70% solids) 15 parts Water 40 parts The viscosity of the resulting mixture was 15,000 centipoise. This mixture was applied on a 420 denier nylon 6.6 airbag fabric substrate using a knife applicator over space and was dried at a temperature of 350 ° F for 3 minutes. The dry coating weight was 0.35 ounce per square yard. The air permeability measured at 125 Pa was 0.0 cfm per square foot of cloth and the lining passed the blocking test. Example 4 Che isat LCH-733X 90 grams NATROSON 250 HHXR 2.5 grams DE-83R 4 grams Water 60 grams The viscosity of the resulting mixture was approximately 15,000 centipoise. This mixture was coated on a 420 denier nylon 6,6 air bag fabric substrate using a knife applicator over space and dried at 350 ° F for 3 minutes. The dry coating weight was 0.3 'ounce per square yard. The air permeability measured at 125 Pa was 0.0 cfm per square foot of cloth and the lining passed the blocking test. Example 5 (Comparative) The same formulation as that used in EXAMPLE 1 was prepared but was applied with a knife in the air bag fabric with a coating weight of 0.55 ounce per square yard. The air permeability was measured again and determined to be 0.0 cfm, as above; however, this coating did not pass the blocking test. Example 6 (Comparative) A coating that was not a cross-linked resin was tested. The formulation was as follows: Micromid 144 LTL (thermoplastic polyamide) 100 grams NATROSOL 250 HHXR 2.6 grams DE-83R 2 grams Water 80 grams The viscosity of the resulting mixture was approximately 15,000 centipoise. This mixture was applied to a 420 denier nylon 6,6 air bag fabric substrate using a knife applicator over space and dried at a temperature of 350 ° F for 3 minutes. The dry coating weight was 0.3 ounce per square yard. This coating passed the blocking test; however, sample fabrics failed the air permeability test by presenting 0.5 to 1 cfm to 125 pa after prolonged standard storage at high temperature in accordance with ASTM D737. Obviously, there are numerous alternative embodiments and modifications of the present invention that are included within the spirit and scope of the following claims.

Claims (1)

CLAIMS A coated base fabric for an air bag comprising a polyester or polyamide substrate fabric coated with a crosslinked elastomeric coating resin; wherein said crosslinked elastomeric coating resin is present in a dry base at a level no greater than about 0.6 ounce per square yard; wherein said crosslinked elastomeric coating resin forms an effective barrier to the air flow such that (a) said coated base fabric exhibits an air permeability level of less than about 0.2 cfm to 125 Pa and (b) two portions of the coated fabric passes the blocking test after prolonged storage in contact with each other, and wherein said crosslinked elastomeric coating resin is selected from the group consisting of butyl rubber, EPDM, polyurethane, hydrogenated NBR, acrylic rubbers, and mixtures thereof. The coated base fabric according to claim 1, wherein said fabric of crosslinked elastomeric coating resin material is present on a dry basis in a coating weight comprised between about 0.1 and 0.5 ounce per square yard of fabric. The coated base fabric according to claim 2, wherein said polyamide substrate fabric is formed of nylon fiber 6,6. The coated base fabric according to claim 1, wherein said substrate fabric is woven from a multiple filament yarn characterized in that it has a linear density of about 210 to 630 denier. The coated base fabric according to claim 4, wherein said multiple filament yarn is characterized by a linear filament density of about 4 denier per filament or less. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coating resin is butyl rubber. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coating resin is EPDM. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coating resin is polyurethane. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coated resin is hydrogenated NBR. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coating resin is present in the form of a latex. The coated base fabric according to claim 1, wherein said crosslinked elastomeric coating resin is present in solution in an organic solvent. An air bag comprising the coated base fabric according to claim

1.